Light steel is a rather vague term, generally can have two kinds of understanding. One is the current "Steel Structure Design Code" (GBJ 17-88) in Chapter XI "round steel, small angle steel light steel structure" refers to the use of round and less than L45 * 4 and L56 * 36 * 4 Light steel structure made of angle steel, mainly in the lack of steel for the time should not be used for the manufacture of reinforced concrete structure of small structure, is now basically not used, so the steel design revision has been basically tend to get rid of. The other one is the single-layer solid portal frame structure with light roof and light exterior wall (also can conditionally use masonry external wall) stipulated in the Technical Code for Steel Structure of Portal Frame Light House. Here the light mainly refers to the envelope is to use lightweight materials. Since the former has been quickly canceled, so now the main meaning of light steel refers to the latter. Light steel structure that is light steel structure building system, is hot-rolled light H steel, light welded steel, high-frequency welded steel, cold-formed thin-walled steel, thin steel and thin-walled steel and other high-performance structural materials and efficient functional materials , In order to assemble various types of high-performance decorative connection materials, can meet the specific use of building features and specific space requirements of the light-weight steel structure of the whole building. Light steel structure and heavy steel structure to determine the structure of steel and light steel structure does not have a unified standard, many experienced designers or project managers are often not fully understand, but we can take some data into account and To determine: 1, plant crane lifting weight: greater than or equal to 25 tons, can be considered heavy steel structure. 2, the amount of steel per square meter: greater than or equal to 50KG / M2, can be considered heavy steel structure.